Power semiconductor module

ABSTRACT

To suppress warpage of a ceramic substrate, and to prevent a reduction in radiation efficiency. 
     A power semiconductor module includes a module casing fitted with a radiator, and a common unit retained by the module casing. The common unit has: a ceramic substrate having a circuit surface disposed with a semiconductor element, and a radiation surface brought into abutting contact with the radiator; and a package formed by exposing the radiation surface and sealing the circuit surface with heat resistant resin. The circuit surface and the radiation surface are respectively formed of metal layers  51  formed on the ceramic substrate, and the metal layer  51  forming the radiation surface has: by forming a buffer pattern  512  including a groove part extending along a circumferential part thereof, a radiation pattern  510  formed on an inner side of the buffer pattern  512 ; and an outer peripheral pattern  511  formed on an outer side of the buffer pattern  512 . Such a configuration enables warpage of the ceramic substrate to be suppressed, and a reduction in radiation efficiency to be prevented.

TECHNICAL FIELD

The present invention relates to a power semiconductor module, and moreparticularly, to a power semiconductor module used for an electricalpower converter such as a converter or inverter.

BACKGROUND ART

As a semiconductor module, there is known a device in which asemiconductor element used for an electrical power converter is sealedwith resin and modularized. In this sort of semiconductor module, a chiparrangement surface of a ceramic substrate is sealed with resin, andheat is radiated from a back surface of the ceramic substrate. For thisreason, if, due to a difference in a thermal expansion coefficientbetween the ceramic substrate and the resin, mold shrinkage of theresin, or warpage of the substrate caused by a heat cycle duringoperation occurs, the occurrence causes a reduction in radiationefficiency, or peeling-off of a semiconductor chip.

Because of this, in a typical semiconductor module, a ceramic substrateon which chip parts including a semiconductor chip are soldered isbonded onto a thick metal plate such as a copper (Cu) or iron (Fe) platethrough a heat spreader or an insulating sheet. Also, a case forsurrounding a chip mounting surface of the ceramic substrate isattached, into which silicon gel is injected to protect the chip parts,and then resin is further filled.

However, in the case where the silicone gel is used to protect the chipparts, moisture intruding from a gap of the case may adversely influencethe chip parts. Also, electrical connections among the chip parts aremade with wire bonding, soldering of a lead frame, or ultrasonicbonding; however, if a part of the bonding is deteriorated by heat orthe like, the use of the silicone gel as a protecting material makes itdifficult to stably fix the wire or lead frame.

For this reason, there has been proposed a semiconductor module in whichresin is directly filled on a chip mounting surface of a ceramicsubstrate without use of the protecting material such as silicone gel(e.g., Patent document 1). In Patent document 1, the ceramic substrateis joined onto a metal plate to form a module substrate on which asemiconductor chip is mounted, and then the resin is injected into aspace surrounded by an enclosing case, a frame body, and a modulesubstrate. If the enclosing case has sufficient stiffness, stress due tomold shrinkage upon curing of the sealing resin can be dispersed intothe module substrate and the frame body to prevent warpage of the modulesubstrate, and therefore temperature cycle resistance can be improved.

Patent document 1; Japanese Unexamined Patent Publication No.1997-237869

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

In a conventional semiconductor module, a ceramic substrate is bonded toa metal plate to thereby prevent warpage of the ceramic substrate andensure a good radiation characteristic. However, in the case of usingthe metal plate, there exists a problem that a reduction in weight ofthe semiconductor module becomes difficult. For this reason, it isconsidered that a radiator is directly fitted onto a back surface of theceramic substrate by employing a configuration in which the warpage ofthe ceramic substrate is unlikely to occur, and omitting the metalplate.

In this case, preferably, to prevent the warpage of the ceramicsubstrate as much as possible, by forming not only on a surface of theceramic substrate a metal layer for mounting a semiconductor chip, butalso a metal layer on a back surface of the ceramic substrate, which isbrought into abutting contact with the radiator, a thermal expansioncharacteristic of the both surfaces of the ceramic substrate are madeuniform.

In the case of forming the metal layers on the both surfaces of theceramic substrate as described above, upon injection of resin onto thesurface of the ceramic substrate after the mounting of the semiconductorchip on the surface of the ceramic substrate, to prevent the resin fromflowing onto the metal layer on the back surface, the resin is injectedwith the back surface of the ceramic substrate being in close contactwith a flat inner surface of a mold. However, even in the case ofinjecting the resin in this manner, a small amount of resin may intrudeonto the metal layer on the back surface of the contact substrate. Inthe case where the resin having intruded onto the back surface of thecontact substrate attaches onto the metal layer on the back surface,radiation efficiency is significantly reduced even if the amount issmall.

The present invention is made in consideration of the above situations,and has an object to provide a power semiconductor module capable ofsuppressing warpage of a ceramic substrate, and preventing a reductionin radiation efficiency.

Means Adapted to Solve Problems

A power semiconductor module according to a first aspect of the presentinvention includes: a module casing fitted with a radiator; and a commonunit retained by the module casing, and is configured such that thecommon unit has: a ceramic substrate having a circuit surface disposedwith a semiconductor element, and a radiation surface brought intoabutting contact with the radiator; and a package formed to expose theradiation surface and to seal the circuit surface with heat resistantresin, the circuit surface and the radiation surface are respectivelyformed of metal layers formed on the ceramic substrate, and the metallayer forming the radiation surface has: by forming a groove partextending along a circumferential part thereof, an inner pattern formedon an inner side of the groove part; and an outer pattern formed on anouter side of the groove part.

Based on such a configuration, the metal layers respectively forming thecircuit surface and the radiation surface are formed on both surfaces ofthe ceramic substrate, and therefore a thermal expansion characteristicof the both surfaces of the ceramic substrate can be made uniform tothereby suppress warpage of the ceramic substrate. Also, between theinner pattern and the outer pattern, the groove part in which any metallayer is not formed is formed, so that even if there is a portion of theresin intruding onto the metal layer to pass through the outer pattern,the portion of the resin is accommodated in the groove part if theportion is small, and therefore does not spread on the inner pattern.For this reason, a reduction in radiation efficiency due to attachmentof the resin onto a surface of the inner pattern can be prevented.

A power semiconductor module according to a second aspect of the presentinvention is, in addition to the above configuration, configured suchthat the groove part is annularly formed along the circumferential partof the metal layer, and thereby the outer pattern surrounds an outercircumference of the inner pattern.

Based on such a configuration, the outer pattern surrounds the outercircumference of the inner pattern with sandwiching the groove part, andtherefore even if a portion of the resin intrudes from any part of theouter pattern, the portion of the resin can be well accommodated in thegroove part. Accordingly, the reduction in radiation efficiency due tothe attachment of the resin onto the surface of the inner pattern can bemore effectively prevented.

Effect of the Invention

According to the present invention, thermal expansion characteristics ofboth surfaces of a ceramic substrate can be made uniform to suppresswarpage of the ceramic substrate. Also, resin intruding onto a metallayer can be accommodated in a groove part, and therefore a reduction inradiation efficiency due to attachment of the resin onto a surface of aninner pattern can be prevented.

BEST MODE FOR CARRYING OUT THE INVENTION

FIGS. 1 and 2 are appearance diagrams illustrating one configurationexample of a semiconductor module 1 according to an embodiment of thepresent invention, in which FIG. 1 illustrates a top surface, and FIG. 2a bottom surface. FIG. 3 is a development perspective view illustratingan appearance upon assembly of the semiconductor module 1.

The semiconductor module 1 is a power semiconductor module intended toconvert AC power and DC power with use of semiconductor elements such asa thyristor, diode, and bipolar transistor. In the present embodiment,as an example of such a power semiconductor module, there is described amodule for achieving a bridge circuit with use of three thyristors andthree diodes. Such a bridge circuit is widely used for a three-phase ACconverter that full-wave rectifies a three-phase AC power supply toconvert it into a DC power supply.

The semiconductor module 1 is configured to contain three common units 3(3 a to 3 c) and two metal plates 4 (4 m and 4 n) in a module casing 2.The common units 3 are units all having a same configuration in which aseries circuit of the thyristor and diode is incorporated, and can beinterchanged for use. Note that, in the present description, componentscorresponding to one another in the three common units are denoted bythe same reference numeral, and if specific components of the commonunits are referred to, symbols “a” to “c” are added to the abovereference numeral.

The module casing 2 includes: a module main body 20 that is formed in athin, substantial box shape, and made of resin; and a module lid 21 thatis formed in a substantially rectangular plate-like body, and made ofresin. The module main body 20 contains therein the three common units 3and two metal plates 4, and has: a top surface opening 22 that opensthroughout the top surface; and three bottom surface openings 23 (23 ato 23 c) that open into parts of the bottom surface. The top surfaceopening 22 is an opening for assembly, which is covered with the modulelid 21 after the assembly, and the bottom surface openings 23 a to 23 care openings for radiation, which respectively expose radiation surfacesof the common units 3 a to 3 c.

The bottom surface of the module casing 2 is a radiator fitting surfacefor assembling a radiator 9. The radiator 9 is a metal casing, radiationfins, or the like, of a device into which the semiconductor module 1 isincorporated, and fitted onto the module casing 2 with use of fittingholes 24 formed at four corners of the module casing 2. The radiationsurfaces of the common units 3 a to 3 c are slightly projected from thebottom surface openings 23 a to 23 c formed in the radiator fittingsurface, and by fitting the radiator onto the module casing 2, can bebrought into close contact with the radiator 9.

On the other hand, a top surface of the module casing 2 is a terminalsurface formed with terminals for connecting external wiring lines, anddisposed with three external terminals 30 (30 a to 30 c), three setscontrol terminals 33 (33 a to 33 c) and 34 (34 a to 34 c), and externalcommon terminals 41 and 42.

The external terminal 30 is a terminal of the common module 3, and thethree external terminals 30 a to 30 c are arranged along one side of themodule lid 21 at regular intervals. The external terminals 30 a to 30 care metal plates that are drawn from gaps of the module main body 20 andmodule lid 21 on the top surface of the module casing 2, and folded soas to be parallel to the top surface of the module casing 2, and extendoutward along the module main body 20, of which end parts are formedwith fastening holes 300.

A top surface of the module main body 20 facing to the fastening holes300 is formed with nut storage parts 200 that store metal nuts so as toprevent them from rotating, and by fastening screws inserted into thefastening holes 300 with the above nuts, the external terminals 30 andexternal wiring lines sandwiched between the above screws and nuts canbe electrically conducted. Note that even if the above nuts are notfastened in the nut storage parts 200, openings of the nut storage parts200 are covered with the external terminals 30 that are folded after thestorage of the nuts, and therefore unless the common units 3 areremoved, the nuts do not drop out of the nut storage parts 200 even whennot fastened with the screws.

The external common terminal 41 is a terminal formed by drawing from themodule casing 2 a part of the metal plate 4 m that electrically conductscommon terminals 31 of the respective common modules 3 a to 3 c to oneanother in the module casing 2, and placed on a side of the module lid21 adjacent to the side along which the external terminals 30 a to 30 care arranged. The external common terminal 41 is, similar to theexternal terminals 30, drawn from gaps of the module main body 20 andthe module lid 21 on the top surface of the module casing 2, and extendsoutward along the module main body 20, of which an end part is formedwith a fastening hole 400. The top surface of the module main body 20facing to the fastening hole 400 is formed with a nut storage part 201that stores a metal nut so as to prevent it from rotating, and byfastening a screw inserted into the fastening holes 400 with the abovenut, the external common terminal 41 and the external wiring linesandwiched between the above screw and the nut can be electricallyconducted. Note that even if the above nut is not fastened in the nutstorage part 201, an opening of the nut storage part 201 is covered withthe external common terminal 41 that is arranged after the storage ofthe nut, and therefore unless the metal plate 4 m is removed, the nutdoes not drop out of the nut storage part 201 even when not fastenedwith the screw.

The external common terminal 42 is a terminal formed by drawing from themodule casing 2 a part of the metal plate 4 n that electrically conductscommon terminals 32 of the respective common modules 3 a to 3 c to oneanother in the module casing 2. The rest of a configuration of theexternal common terminal 42 is exactly the same as that of the externalcommon terminal 41.

The control terminals 33 and 34 are terminals of the common modules 3 (3a to 3 c), and the three sets of two control terminals 33 a to 33 c and34 a to 34 c are arranged along a side of the module lid 21 on a sideopposite to the side along which the external terminals 30 are arranged.The control terminals 33 and 34 are pin-like terminals of which crosssections extending upward are substantially rectangular shaped, anddrawn outside the module casing 2 through guide holes 210 of the modulelid 21.

Next, with use of FIG. 3, an example of a method for assembling thesemiconductor module 1 is described. The common unit 3 is incorporatedin the module main body 20 from the bottom surface opening 23, and theexternal terminal 30 thereof is folded outward with the common unit 3being inserted to an innermost position. If the three common units 3 ato 3 c are attached in this manner, they can be contained in the modulemain body 20 in a state where they are arrayed such that longer sidesthereof face to each other at regular spaces.

The metal plates 4 m and 4 n are incorporated in the module main body 20from the top surface opening 22. The metal plates 4 m and 4 n arearranged with intersecting with a longitudinal direction of the commonunit 3 so as to respectively traverse all of the common units 3 a to 3c. Also, the metal plate 4 m is formed with three fastening holes 401 ato 401 c, and with use of screws, fastened with and electricallyconducted to all of the common terminals 31 of the common modules 3.Similarly, the metal plate 4 n is formed with three fastening holes 402a to 402 c, and with use of screws, fastened with and electricallyconducted to all of the common terminals 32 of the common modules 3.Subsequently, closing the top surface opening 22 with the module lid 21completes the assembly of the semiconductor module 1.

FIG. 4 is a diagram illustrating one configuration example of an insideof the common module 3, in which (b) is a diagram as viewed from adirection B illustrated in (a). An upper surface of a ceramic substrate50 is arranged with semiconductor elements 54 and the terminals 30 to34, and used as a circuit surface for connecting them, whereas a lowersurface of the ceramic substrate 50 is used as a radiation surface thatis brought into close contact with a heat-transfer surface of theradiator 9.

The ceramic substrate 50 is a circuit board that is formed on the bothsurfaces thereof with metal layers 51 and 52, and for example, copper(Cu) thin plates are fixed by a DBC (Direct Bonding Copper) method. Themetal layer 52 on a circuit surface side is patterned with use of aphotolithography technique, and used as wiring. Also, by forming themetal layer 51 on a radiation surface side as well, a thermal expansioncharacteristic of the both surfaces of the ceramic substrate 50 are madeuniform to suppress warpage of the ceramic substrate 50.

The semiconductor chips 54 are arranged on the metal layer 52 through asolder layer 53. We herein assume that, as the semiconductor chips 54,the thyristor and the diode connected to each other in series arearranged. Also, although omitted in the diagrams, the other electronicparts such as a chip resistor are arranged as necessary. Further, therespective terminals 30 to 34 are also disposed on the metal layer 52through the solder layer 53, or on the semiconductor chips. Betweenthese electronic parts and the respective terminals 30 to 34, electricalconnections are made with use of the metal layer 52 pattern, bondingwires, or lead frame as necessary. Also, the respective terminals 30 to34 are sandwiched between two molds during resin molding, and thereforefolded so as to be parallel to the ceramic substrate 50 at positions ofwhich heights from the ceramic substrate 50 are the same.

FIG. 5 is a diagram of the ceramic substrate 50 in FIG. 4 as viewed froma lower surface side. The metal layer 51 formed on the lower surface ofthe ceramic substrate 50 includes a rectangular shaped radiation pattern510 having a large area, and an elongated outer circumferential pattern511 surrounding the radiation pattern 510, and between the radiationpattern 510 and the outer circumferential pattern 511, there is formed abuffer pattern 512 in which the metal layer 51 is not formed. That is,the buffer pattern 512 is formed as an elongated groove part, forexample, a groove part having a constant width, surrounding theradiation pattern 510 on an inner side of the outer circumferentialpattern 511. For the formation of such a pattern, for example, aphotolithography technique can be used.

Based on such a configuration, with respect to the buffer pattern 512 asthe groove part extending along a circumferential part of the metallayer 52 on the radiation surface side, the radiation pattern 510 isformed inside the buffer pattern 512 as an inner pattern, and the outercircumferential pattern 511 is formed outside the buffer pattern 512 asan outer pattern.

Note that, in this example, there is illustrated a configuration inwhich along a circumferential part of the metal layer 52 on theradiation surface side, the annular buffer pattern 512 is formed alongthe circumferential part of the metal layer 52 on the radiation surfaceside such that the outer circumferential pattern 511 surrounds an outercircumference of the radiation pattern 510 with sandwiching the bufferpatter 512; however, without limitation to such a configuration, theremay be a configuration in which the buffer pattern 512 is formed alongonly a part of the circumferential part of the above metal layer 52. Inthis case, it is only necessary to have a configuration in which thegroove part is formed along at least one side of the rectangular shapedmetal layer 51, and in the case where the metal layer 51 is rectangularshaped, there may be a configuration in which the groove part is formedalong any one of a pair of longer sides or a pair of shorter sidesfacing to each other.

The ceramic substrate 50 formed with the circuit is sealed by the resinwith the metal layer 51 of the ceramic substrate 50, and the end sidesof the respective terminals 30 to 34 being only unsealed. The sealing isperformed by, for example, an RTM (Resin Transfer Molding) method usingheat curable epoxy resin. On the basis of such resin molding processing,there is formed a package 35 in which the metal layer 51 is exposed, andthe terminals 30 to 34 are projected. The resin molding processing isperformed with the lower surface of the ceramic substrate 50 being inclose contact with a flat inner surface of the mold to as to prevent theresin from flowing onto a surface of the metal layer 51. Also, thebuffer pattern 512 is preliminarily formed, so that even if there existsa portion of the resin that intrudes onto the metal layer 51 and passesthrough the outer circumferential pattern 511, it is accommodated in thebuffer pattern 512 as the groove if an amount of it is small, andtherefore the resin does not spread on the radiation pattern 510. Forthis reason, a reduction in radiation efficiency due to attachment ofthe resin onto a surface of the radiation pattern 510 can be prevented.

In particular, in the present embodiment, the outer circumferentialpattern 511 surrounds the outer circumference of the radiation pattern510 with sandwiching the buffer pattern 512, and therefore even if theresin intrudes from any part of the outer circumferential pattern 511,the resin can be well accommodated in the buffer pattern 512.Accordingly, the reduction in radiation efficiency due to the attachmentof the resin onto the surface of the radiation pattern 510 can be moreeffectively prevented.

FIGS. 6 and 7 are appearance diagrams illustrating one configurationexample of the common unit 3 after the resin sealing, in which FIG. 6(a) illustrates a top surface, and (b) a bottom surface. Also, FIG. 7(a) illustrates a side surface as viewed from a common terminals 31 and32 side, (b) a side surface as viewed from an external terminal 30 side,and (c) a side surface as viewed from the control terminals 33 and 34side, respectively.

FIG. 8 is an appearance diagram illustrating one configuration exampleof the common unit 3 before the common unit 3 is contained in a modulecasing 2, in which a state where the respective terminals 30 to 34 arefolded is illustrated. In addition, in the diagram, (a) illustrates atop surface, and (b) a side surface as viewed from the common terminals31 and 32 side. The external terminal 30 and the control terminals 33and 34 are orthogonally folded, and face upward, and the commonterminals 31 and 32 are folded at an angle of 180 degrees, and extendalong a top surface of the middle of the package 35.

The respective terminals 30 to 34 after the resin sealing are allexposed outside the package 35 from valley lines of step parts openingupward, in the example illustrated in the diagram, from deepest parts ofconcave portions on the package 35 formed by the top surface and theside surfaces, and extend outward along the top surface of the package35. Applying upward force to ends of these terminals 30 to 34 to foldthe terminals 30 to 34 at around the above valley lines results in ashape illustrated in FIG. 8. In this case, a below folded part of therespective terminals 30 to 34, top surfaces 320 to 323 extending outwardare formed, and these surfaces function as insulating walls. That is, byfolding the terminals 30 to 34 at positions receding from edge parts ofthe package 35, the projecting portions 320 to 323 of the package can beformed below the terminals 30 to 34 to elongate creepage distances fromthe radiator 9 to the terminals 30 to 34, and therefore insulationproperties can be improved.

Note that, in FIG. 6 (a), hatched base parts of the respective terminals30 to 34 are formed so as to be embedded in the top surfaces 320 to 323of the package with only top surfaces thereof being exposed. Such aconfiguration can be achieved if the resin molding processing isperformed with the respective terminals 30 to 34 being in close contactto the inner surface of the mold for forming the top surfaces 320 to 323of the package.

If, upon folding of the terminals 30 to 34, the terminals 30 to 34 andthe top surfaces 320 to 323 cannot be easily separated from each other,the package 35 cracks, or the terminals 30 to 34 are folded outside thevalley lines, resulting in a reduction in quality of the common unit 3.For this reason, the cross sections of the terminals 30 to 34 are formedin a shape that facilitates peeling off from the top surfaces 310 to313, i.e., a shape in which a width becomes narrower as it goesdownward. Specifically, side surfaces of the terminals 30 to 34 aretapered, and thereby the cross sections of the terminals 30 to 34 areformed in a trapezoidal shape that widens upward. Any shape other thanthe trapezoidal shape is possible if the shape has a cross section ofwhich a width widens upward, such as a triangular or semicircular shape.Also, the top surfaces of the terminals 30 to 34 are exposed surfacesfrom the top surfaces 320 to 323, and are therefore desirably plainsurfaces. In addition, it goes without saying that the portionsseparated from at least the top surfaces 320 to 323 desirably have sucha cross-sectional shape.

An end part of the common terminal 31 is formed with a fastening hole301 for fastening the metal plate 4 m. On the top surface of the package35 facing to the fastening hole 301, a nut storage part 311 that storesa metal nut so as to prevent it from rotating is formed as a concaveportion. Accordingly, by fastening a screw inserted into the fasteninghole 301 and the fastening hole 401 of the metal plate 4 m with theabove nut, the common terminals 31 and the metal plate 4 m sandwichedbetween the above screw and nut can be electrically conducted. Note thateven if the above nut is not fastened in the nut storage part 311, anopening of the nut storage parts 311 is covered with the common terminal31 that is folded after the storage of the nut, and therefore the nutdoes not drop out of the nut storage part 311 even when not fastenedwith the screw.

In exactly the same manner, an end part of the common terminal 32 isformed with a fastening hole 302 for fastening the metal plate 4 n. Onthe top surface of the package 35 facing to the fastening hole 302, anut storage part 312 that stores a metal nut so as to prevent it fromrotating is formed as a concave portion. Accordingly, by fastening ascrew inserted into the fastening hole 302 and the fastening hole 402 ofthe metal plate 4 n with the above nut, the common terminal 32 and metalplate 4 n sandwiched between the above screw and the nut can beelectrically conducted. Note that even if the above nut is not fastenedin the nut storage part 312, an opening of the nut storage part 312 iscovered with the common terminal 32 that is folded after the storage ofthe nut, and therefore the nut does not drop out of the nut storage part312 even when not fastened with the screw.

Also, the package 35 is formed in a thin, substantially rectangularshape, and side surfaces of the package 35 are provided with taperedparts 36, which makes an outer shape of the package 35 larger toward atop surface side, as compared with that of the bottom surface on whichthe radiation surface is formed. Also, on the top surface of thepackage, the nut storage holes 311 and 312 are formed as the concaveportions, and in the portions, a resin layer is formed thin.Accordingly, the stress acting on the ceramic substrate 50 due to moldshrinkage of the resin is suppressed, and therefore the warpage of theceramic substrate 50 can be reduced.

FIGS. 9 and 10 are appearance diagrams only illustrating the module mainbody 20 of FIG. 1, in which FIG. 9 illustrates the top surface, and FIG.10 the bottom surface. In an internal space of the module main body 20,one reinforced beam 25 on a top surface side, which traverses the commonunits 3 a to 3 c, and two reinforced beams 26 on a bottom surface side,which intersect with the reinforced beam 25, are formed. The reinforcedbeam 25 is arranged further above the common units 3 a to 3 c, whereasthe reinforced beams 26 are formed between adjacent two of therespective common units 3 a to 3 c, and position the common units 3 in ahorizontal plane.

Unit abutting contact parts 27 and 28 are projecting portions formed onan inner wall of the module main body 20 or step parts opening downward,and brought into abutting contact with both longitudinal ends of thecommon unit 3 to thereby position the common module 3 in a verticaldirection.

FIG. 11 is a cross-sectional diagram for a case where the semiconductormodule 1 fitted with the radiator 9 is cut along a section line A-A inFIG. 10. When the fitting holes 24 are used to fit the radiator 9 ontothe module casing 2, the radiator fitting surface of the module casing 2and the flat heat-transfer surface 91 of the radiator 9 can be made toface to each other, and brought into a state where the both are as closeto each other as possible. At this time, the common unit 3 is retainedby the module casing 2 such that the radiation surface thereof isslightly projected from the bottom surface opening 23 of the modulecasing 2, and therefore sandwiched between the unit abutting contactparts 27 and 28 and the heat-transfer surface 91 of the radiator. Forthis reason, the radiation surface of the common unit 3 can be broughtinto close contact with the heat-transfer surface 91 of the radiator 9.

FIG. 12 is an explanatory diagram illustrating an example for a casewhere warpage occurs in the ceramic substrate 50. The package 35 made ofthe resin has a large thermal expansion coefficient as compared with theceramic substrate 50. For this reason, upon cooling after the resinmolding processing, the package 35 more largely shrinks as compared withthe ceramic substrate 50, and therefore downward convex warpage islikely to occur in the ceramic substrate 50, which is referred to as“positive warpage”. On the other hand, upward convex warpage of theceramic substrate 50 is referred to as “negative warpage”. From theperspective of radiation efficiency, the occurrence of the warpage isnot desirable, and in particular, in the case of the negative warpage,because the middle part of which a temperature is increased is notbrought into close contact with the radiation plate, the radiationefficiency is significantly poor as compared with the case of thepositive warpage.

In the semiconductor module 1 in FIG. 1, the three common units 3 a to 3c are arrayed in the substantially rectangular module casing 2, andtherefore a temperature of the central common unit 3 b is furtherincreased as compared with the common units 3 a and 3 c on both sides.On the other hand, the radiator 9 is fitted with use of the fittingholes 24 provided at the four corners of the module casing 2, andtherefore as compared with the common units 3 a and 3 c on the bothsides, pressing force of the radiator 9 on the radiation surface 51 ofthe central common unit 3 b is small, which is likely to cause poorradiation efficiency. Accordingly, for the central common unit 3 b, theceramic substrate 50 having a more positive warpage property isdesirably used as compared with the common units 3 a and 3 c on the bothsides. In particular, the ceramic substrate 50 of the central commonunit 3 b desirably has a positive warpage property.

Note that, in the above embodiment, the metal plates 4 m and 4 n areused to respectively connect the common terminals 31 and 32 of therespective common units 3 a to 3 c in the module casing 2; however, thepresent invention is not limited to such a case. That is, instead of themetal plates 4 n and 4 m, a metal block having an arbitrary shape can beused.

Also, in the above embodiment, there is described the example where thecommon unit 3 includes the thyristor and the diode; however, the presentinvention is not limited to such a case. That is, the common unit 3 caninclude a combination of a diode, a thyristor, a bipolar transistor, andany other power semiconductor element. For example, the common unit 3may include a series circuit of two thyristors. Also, the presentinvention is not limited to a case where the common unit 3 includes twosemiconductor elements.

Further, in the present embodiment, there is described the example ofthe three-phase AC converter in which the semiconductor module 1converts the three-phase AC power into the DC power; however, thepresent invention is not limited to such a case. For example, thepresent invention can also be used for an inverter that converts a DCpower into an AC power, or the other power converter.

Still further, in the present embodiment, there is described the exampleof the semiconductor module 1 that contains the three common units 3 inthe module casing 2; however, a module casing containing only one commonunit 3 can be achieved. In this case, the metal plates 4 m and 4 nbecome unnecessary. The common unit 3 can be made common tosemiconductor modules respectively containing different numbers ofcommon units 3 in this manner, and therefor cost can be further reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an appearance diagram illustrating one configuration exampleof a semiconductor module 1 according to an embodiment of the presentinvention, in which a top surface of the semiconductor module 1 isillustrated.

FIG. 2 is an appearance diagram illustrating the one configurationexample of the semiconductor module 1, in which a bottom surface of thesemiconductor module 1 is illustrated.

FIG. 3 is a development perspective view illustrating an appearance uponassembly of the semiconductor module 1 of FIG. 1.

FIG. 4 is a diagram illustrating one configuration example of an insideof a common module 3.

FIG. 5 is a diagram of a ceramic substrate 50 in FIG. 4 as viewed from alower surface side.

FIG. 6 is an appearance diagram illustrating one configuration exampleof the common unit 3 after resin sealing, in which a top surface and abottom surface of the common unit 3 are illustrated.

FIG. 7 is an appearance diagram illustrating the one configurationexample of the common unit 3 after the resin sealing, in whichrespective side surfaces of the common unit 3 are illustrated.

FIG. 8 is an appearance diagram illustrating one configuration exampleof the common unit 3 before the common unit 3 is contained in a modulecasing 2.

FIG. 9 is an appearance diagram only illustrating a module main body 20of FIG. 1, in which a top surface of the module main body 20 isillustrated.

FIG. 10 is an appearance diagram only illustrating the module main body20 of FIG. 1, in which a bottom surface of the module main body 20 isillustrated.

FIG. 11 is a cross-sectional diagram for a case where the semiconductormodule 1 fitted with a radiator 9 is cut along a section line A-A inFIG. 10.

FIG. 12 is an explanatory diagram illustrating an example for a casewhere warpage occurs in the ceramic substrate 50.

1. A power semiconductor module comprising: a module casing fitted witha radiator; and a common unit retained by said module casing, whereinsaid common unit has: a ceramic substrate having a circuit surfacedisposed with a semiconductor element, and a radiation surface broughtinto abutting contact with said radiator; and a package formed to exposesaid radiation surface and to seal said circuit surface with heatresistant resin, said circuit surface and said radiation surface arerespectively formed of metal layers formed on said ceramic substrate,and said metal layer forming said radiation surface has: by forming agroove part extending along a circumferential part thereof, an innerpattern formed on an inner side of said groove part; and an outerpattern formed on an outer side of said groove part.
 2. The powersemiconductor module according to claim 1, wherein said groove part isannularly formed along the circumferential part of said metal layer, andthereby said outer pattern surrounds an outer circumference of saidinner pattern.